1. Field of the Invention
This invention relates to catalysis. In one aspect, the invention relates to antimony-containing phosphomolybdic oxide catalysts while in another aspect, the invention relates to the use of these catalysts in the oxidation of oxygenated C.sub.4 hydrocarbons to methacrylic acid.
2. Description of the Prior Art
The art is replete with various phosphomolybdic oxide catalysts useful for the oxidation of oxygenated C.sub.4 hydrocarbons, such as methacrolein, isobutyraldehyde, t-butyl alcohol, etc. Representative of this art are U.S. Pat. Nos. 4,301,031; 4,301,030; 4,271,040 and 4,238,359. While the catalysts used in each of these teachings are all promoted phosphomolybdic oxide catalysts, they differ from one another primarily in the definition and combination of promoter elements. For example, the catalysts of U.S. Pat. No. 4,271,040 must contain at least one of cesium and calcium while the others can contain any alkali metal. As a further example, while the catalysts of these teachings can contain a combination of copper and vanadium, only U.S. Pat. Nos. 4,301,030 and 4,301,031 must contain this combination.
Although the catalysts of these references are generally quite good for their intended purpose, all are subject to improvement in methacrylic acid selectivity and catalyst life.